text:
If a pilot has the wrong altimeter setting, will his transponder mode C altitude be off too?
Just wondering if the transponder mode C reported altitude will be off if the pilot accidentally has the wrong altimeter setting.

No, the altimeter is not connected to the transponder in any way (on most GA aircraft)

No your altimeter setting has no effect.
The altitude signal for mode C comes from a separate pressure altitude sensing "blind" encoder that only supplies the transponder, or an equivalent device integrated into the transponder itself, or a pressure altitude signal coming from an Air Data Computer on a larger aircraft.  It reports pressure altitude to a resolution of 100 ft.  So as you are climbing between 1000 and 1100 ft, ATC's indication will roll over from 1000 to 1100 at somewhere around 1050ft, from 1100 to 1200 somewhere around 1150 ft, etc.
So if you make the wrong altimeter setting and level at a cleared altitude and the pressure altitude reported by your transponder is off by more than 1 or 200 feet from the pressure altitude they expect to see, ATC will inquire about your altimeter setting.


text:
What does the ASDE-X ground radar unit look like?

Above is a picture of a primary / secondary surveillance radar combo (top is secondary, bottom is primary).
What does the ASDE-X radar unit look like in real life?

It isn't one instrument, it is the integration of multiple sources, such as the radar picture you posted, antennas, GPS, and ADS-B signals, so there is no "picture" of an "ASDE-X radar unit".

This page claims to show the Raetheon ASDE antenna at Boston Logan. However, Saab Sensis appears to be the prime contractor for the ASDE-X system. Boston does have an ASDE-X system, according to the FAA.

According to the above link, Saab provides the "Multi-Sensor Data Processor" that "fuses the surface movement radar, multilateration, ADS-B and terminal radar data into a single track that is correlated with flight plan information." So my guess is that Raetheon provides the radar antenna and Saab does the software integration, alerting, fusing, etc. Since the contract is in the US there may have been a requirement to use a US radar supplier.
As an interesting aside, Saab recently announced a third generation Surface Movement Detection antenna, the SR-3:

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
What does the "T" on sectional charts mean in reference to airspace altitude?
These are present in the San Francisco class bravo / Oakland class charlie and O'Hare class bravo / Midway class charlie.

T is used to signify that the top of Class C airspace that lies under Class B is the bottom surface of that airspace. This is important when the Class C segment lies under multiple layers of Class B, where no single top altitude applies.

So the T / 15 that I circled in blue in the north portion means that between 1500 and up to (but not including) 2100 feet MSL is the Oakland class charlie. And on the north side of that blue arc of the T / 15 is Oakland class charlie that begins at 1500' and goes up to (but not including) 3000 feet MSL?

@jeff0000 Correct. T is particularly important when under multiple layers of Class B.

You can start many "what does this thing on an FAA chart mean" questions with the FAA's Aeronautical Chart User's Guide.  It doesn't go into a deep explanation, but does show it as an example in this case.
The symbol can be found on page 17 of the 2018 guide.

 The figure at left identifies a sector that extends from the surface to the base of the Class B.

Since the Class C airspace is sandwiched between the surface and the shelves of the nearby Class B airspace, the T indicates that the upper limit of the ClassC surface area is on the bottom of the overhead Class B shelf.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Does the Cessna 152 have a name?
I'm wondering if the Cessna 152 has a name? There's the Cessna Skyhawk 172 and the Cessna Skylane 182.

Informally, "Skychicken"

Cessna started to apply marketing names to their line in the early 60s (along with goofy marketing gimmicks like the "Land-O-matic" name for the spring steel gear).  Up to then they were just known by model numbers.  The 150 was the "Commuter". For some reason the name wasn't applied to the 152 (which is a 150 with a Lycoming engine), which just has the model number.

But there was a variant called the 152 Aerobat, but in this case the name was to distinguish it from the basic 152.

Aerobat was also for the 150, when the aerobatic model came out in 1970. Why they kept the marketing name only for the aerobatic version when the Lyc engine was done to create the 152 is a mystery.

Originally, only C172s with the deluxe option package were "Skyhawks"; the base models weren't.  They got rid of the base model in 1976, so only Skyhawks (and the new Skyhawk II, with a more deluxe option package) remained.  Likewise, the C182A was technically the first Skylane because the original C182 (no letter) wasn't called that.  TL;DR: Cessna naming is a mess.

The 152 with the 125 hp engine modification is known as the Sparrow Hawk. Although, I'm not sure if that is an official name given by Cessna.

No that's an STC name.


text:
Twin engine helicopters: is the throttle controlled separately for each engine or together?
There is usually a twist throttle on the collective for a single engine helicopter. On twin engine helicopters, does the twist throttle control it for both engines, or just for one?

Most employ separate throttles, either twist-type, on the collective or levers in an overhead quadrant.
Bell products use duel collective mounted, twist type throttles, in series. Sikorsky uses overhead levers. French SA > AS > Eurocopter > Airbus > Leonardo use levers overhead. Agusta uses overhead levers.

@Walker, are there two separate twist type throttles, or just one (that controls both engines) on Bell helicopters?

@jeff0000 Yup. Sorry. Bells use two separate twist throttles, in series (See Edit). I don't remember which engine corresponds to the more forward twist-grip vs the more aft twist-grip.


text:
Where is the radio PTT button on a Robinson R22 helicopter?
I have some combination of joysticks and a rudder that I'm trying to use for helicopter flight simulation on my PC. Where is the radio PTT button on a Robinson R22 helicopter?

You can't realistically mimic the feel of the R22 controls with a joystick because it's an unusual configuration. I've done both simulated and the real thing so trust me when I say it's going to be radically different. This is the Robinson R22 control column:

The R22 has a bent T shaped control arrangement with the control column in between the 2 seats. The T is connected at the pivot point (green arrow), the handling pilot pulls the stick down towards their lap, pulling the other side up. Instructors have to learn to fly with their arm in the air sometimes. The red arrow points to the intercom and PTT buttons. The intercom button is not always there, newer versions generally have a voice activated (VOX) intercom so no button is required.
The blue arrow points to the pin to remove the left hand controls. In most helicopters the pilot sits on the right, if you have a non-flying passenger it may be good to remove the controls so they can't accidentally grab it. The left side pedals are removable too.


text:
What are the helicopter frequencies on the LA heli charts used for?
The LA heli charts list frequencies for the different heli routes in LA:

Are the frequencies used as a "CTAF" for helicopters, or is there an air traffic controller on that frequency telling helicopters what to do? I'm also wondering if the helicopter freq 119.80 at LAX issues class bravo transitions?

This is the frequency for the tower controller who is due to control inbound helicopters. You can see LAX 119.8, HHR 121.1 and LGB 120.5 frequencies noted. These are all frequencies used by the tower controller at these aerodromes.
At LAX, the class bravo transition will be issued by the tower controller on 119.8.

Thanks. If we're talking to Hawthorne on their helicopter frequency, would we ring up "Hawthorne Tower" or "Hawthorne Helicopters"? Also, is the bravo transition on 119.8 only for helicopter shoreline routes, or do mini route transitions also use 119.8?

Hawthorne Tower is the callsign of the position working you. 119.8 Should be for anyone looking to transition the bravo.


text:
Is altitude and heading your discretion when you are cleared visual approach?
If I'm north of KSAN heading east and the controller clears me for the visual approach for runway 27, can I descend and turn the plane at my discretion so that I  can get ready for landing?
Also, once a controller clears me for the visual approach and I accept it, am I responsible for my own terrain and obstruction clearance?

Are you flying VFR? If so, then yes...

Same if you're IFR in VFR conditions.

@RonBeyer If you're cleared visual approach, it implies that you're on an IFR flight plan as far as I know.

Sweetwater visual for 27: https://aeronav.faa.gov/d-tpp/1902/00373SWEETWATER_VIS27.PDF

only requirement I can remember for visual app is to stay above minimum radar alt. You are responsible for both trafffic and ground separation,  but atc still needs to have you on radar

@Radu094 that's absolutely false, visual approaches in non-radar environments are common.

@pericynthion hmm...well, that’s true. Let me check the docs and see where this radar ideea comes from...

@Radu094. Nope. ATC Remains responsible for separation during a visual approach, unless an aircraft has specifically been instructed to maintain visual separation to another.

well, if ATC maintains separation, then that would be a good reason to stay in radar contact, so I remembered something fuzzy....Now why can’t I find my docs on visual approaches? Hold on, I need to get home to my desktop. edit: also just remembered noise abatement proc (if any) must still be respected in visuals.

Visual approach procedures are discussed in AIM 5-4-23. A visual approach is an IFR procedure and you must be on and stay on an IFR flight plan. It authorizes you to proceed visually clear of clouds to the airport. You may make whatever normal maneuvers necessary to safely conduct the approach and landing including descents and turns. Under most conditions, you are responsible for your own terrain clearance and separation. The exception is if you have the airport in sight but not the aircraft you're following. ATC can still clear you for the visual but will retain radar separation responsibility.
Note that a visual approach is different from a "Charted Visual Approach Procedure," which KSAN happens to have for Runway 27. If cleared for the charted visual, then you must fly it as depicted.


text:
What does "<aircraft type> X miles in trail, runway 25R cleared to land" mean?
I was listening to the LiveATC Phoenix North Tower feed as he was clearing aircraft to land. He said something like "Southwest fifteen sixty five, Phoenix Tower, (aircraft type), X miles in trail, runway 25R, cleared to land".
What does the "(aircraft type) X miles in trail" portion mean?
Is the controller pointing out the aircraft behind the aircraft that is being given the landing clearance? If yes, why would the aircraft in front care?

how clearly did you hear it? Its possible they said Southwest 1565T 25 miles inbound runway 25R cleared to land

100%. He didn't do this once. He used the same phraseology more than 10 times with succeeding arrivals.

I still think something is being misheard here. If the OP hears this on PHX tower again, I'd be curious of the time so I can listen myself and provide the most correct answer...

The controller's telling Southwest 1565 it's cleared to land (otherwise they would use the other aircraft's identification), and by the way there is an airplane of a certain type coming up behind and to take that into consideration in the event that Southwest 1565 was thinking of spending too much time on the runway after landing instead of promptly getting out of the way.
That kind of comment added to the landing clearance suggests that the airplane behind is a little closer than usual, or is going significantly faster, or it's just really busy with airplanes spaced at minimum separation, and Southwest should expedite clearing the runway.

This is standard phraseology, and is in the pilot controller glossary. It may also be expressed in "minutes in trail".

In light of the new answer that is in direct contradiction to yours, do you have some references to support your claim?

I highly doubt you heard the controller correctly, or understood what he was actually saying. Sometimes, the words are spoken quickly and to a novice, is illegible. Also, LiveATC radios are volunteer hosted and not the same as what controllers and pilots actually hear.
I suspect the controller was issuing the traffic AHEAD of the landing traffic. Typically tower controllers issue the traffic AHEAD in the sequence, not behind. I highly doubt a controller would expect a pilot to "figure out" that the mileage call for someone behind him meant he needed to expedite off the runway. Rather, it would include some "slang" language, "expect no delay off the runway, traffic is close behind." If it was being issued multiple times and you heard it repeatedly, you likely heard him letting the trailing aircraft how far behind the traffic ahead of them they were. Lastly, the controller may have been omitting (or you weren't hearing) a key word in the clearance that changed the context. I highly doubt the controller was issuing the trailing traffic to the leading traffic 10+ times in a row.

Welcome to [Aviation.SE]! While your argument sounds reasonable, it is in direct conflict with the (current) other answer indicating that this is standard phraseology. Do you have any references to back up your claim? (Granted, there are no references to back the other claim, either.)

I don't have a reference because it's purely a technique used by air traffic controllers, neither is required beyond the "Standard phraseology" of issuing traffic (as cited a little out of context) in the above answer.I suspect any "reference" provided to the contrary will be out of context. If we could hear the actual tapes (OP could provide the date/time they were listening) we could "hear the evidence" for ourselves, as I believe the OP misheard the controller.

It might be possible the controller was advising in case of a wake turbulence encounter. I once sat the jumpseat of a CRJ2. We were getting bumped around a bit on final and the captain asked who we were following... a B738, four miles in trail. Good to know I suppose. If the controller was doing this for every arrival that seems like extraneous phraseology though—I would expect it to be issued for a large behind a heavy, or a small behind a large, but not every single inbound.

at some of the more airline-based towers it seems to be a technique thing, do it for everybody and not worry about it or think about who you issued it for vs who you didn't. It certainly could've been, but controllers are blissfully unaware of the affects of wake turbulence beyond a lesson in a computer lesson every couple years when someone screws it up. Good food for thought though.


text:
Do large cities contain enough iron to significantly affect an aircraft's magnetic compass?
In most areas of the world, the magnetic compass is the ultimate heading reference.  Although pilots look to the directional gyro most of the time when flying (because the directional gyro's reading is unaffected by the aircraft's pitch and bank attitude, unlike the magnetic compass), the directional gyro has to be periodically reset by reference to the magnetic compass,1 as the gyro's reading drifts over time due to a combination of

friction in the gyro mechanism, and
the fact that, as the earth is not an infinite stationary flat plane,

an aircraft travelling in a straight line over the earth's surface will see a slow change in heading as its position relative to the earth's poles changes, while the directional gyro, which uses the aircraft's frame of reference, thinks that heading remains constant in straight flight, and
the reading from a directional gyro on the earth's surface will cycle slowly throughout the course of the day as the earth rotates underneath it,2 while, because the earth's magnetic field rotates with the earth, a magnetic compass will experience no such precession.

Magnetic declination (the angle between true north and magnetic north, which is useful to know because maps are generally referenced to true north and because the direction of magnetic north shifts over time due to changes in the earth's magnetic field) changes as you fly from place to place.  Part of this change is due to a combination of the earth (and its magnetic field) not being an infinite flat plane and of flow irregularities in the earth's liquid outer core (the source of the earth's magnetic field3); these changes are gradual and only matter much over long distances.  However, some areas have large local irregularities in magnetic declination, due to large deposits of magnetic material in the ground (mostly the aptly-named magnetite, but some other iron-bearing minerals are also naturally magnetic and play a part in this).  These large ore bodies, acting as giant magnets, cause magnetic declination to rapidly spike or swing as one passes over or through the area.  For reasons that are hopefully obvious, these types of areas are marked on aeronautical charts used in air navigation.
Huge quantities of magnetic material are also found in large cities, primarily in the form of refined iron and steel alloys, alongside many possible sources of magnetization potentially orders of magnitude stronger than that from the earth's magnetic field (such as the magnetic fields produced by energized electrical-power-transmission lines or by lightning strikes on tall buildings, the use of powerful electromagnets in construction and heavy industry, and the ubiquitous use of weaker electromagnets and permanent magnets in electrical motors and generators, including the huge generators that energize the power grid).  Additionally, while most areas with large local magnetic-declination variations are small enough to be flown through fairly quickly (minimizing the error picked up by the directional gyro while passing through the aforementioned area, and, thus, allowing one to simply "fly the gyro" and ignore the magnetic-compass indications until out of the magnetically-deviant area), the airspace in and near large cities has the potential to keep aircraft in the local airspace for prolonged periods (approaches, traffic circuits, holding patterns) and also tends to require more accurate and precise navigation to keep aircraft from colliding with each other or with the ground or ground-mounted obstacles, both of which would make relying on the drifting directional gyro4 increasingly risky and increase a pilot's reliance on their magnetic compass.
Is the iron and steel content of large modern cities great enough to significantly affect an aircraft's magnetic compass?

1: The exception to this is in areas near the earth's magnetic poles, where the earth's magnetic field points mostly straight up and down (making magnetic compasses unreliable), aircraft navigation uses true heading rather than magnetic, and the directional gyro itself serves as the heading reference and is set by other means (GPS or IRS if so equipped, otherwise by reference to ground landmarks or celestial navigation).
2: The effect of the earth's rotation on a spinning gyroscope can itself be useful; this is the basis of the marine gyrocompass, which exploits this to create an instrument that can reliably point to true north for as long as the earth continues to rotate.  However, this alignment to true north is fairly slow and depends on the gyroscope's position in space continuing to move in, or very close to, the same direction as the earth's surface, and aircraft change position relative to the earth's surface too rapidly for a gyrocompass to be useful.  Additionally, most gyrocompasses are weighted to keep the gyrocompass horizontal and allow the gyroscope to precess properly; the use of weights for this purpose requires that the direction of apparent down relative to the earth's surface remain essentially constant, which is almost always true on the large marine vessels generally equipped with gyrocompasses, and is never true on an aircraft except in perfectly-straight-and-level-and-unaccelerated flight.
3: Although a significant fraction of the earth's magnetic field is contributed by magnetic materials in the earth's crust, this is itself a result of these materials having been bathed in the magnetic field of the earth's core.
4: While an aircraft flying within a small area for an extended period of time will not experience the gradual change in direction-versus-heading produced by flying long distances over the earth's curved, finite surface, it will still accumulate directional-gyro error due to friction within the gyro and to the earth rotating under the aircraft and its gyro.

A single steel building does, if the aircraft flies close enough, never mind a city core like those of New York or Chicago.
However, the amount of steel isn't the whole story.  Each I-beam, sheet of corrugated, or length of rebar has its own magnetic field, mostly determined by its orientation the last time it cooled below its Curie point -- and no effort is made to align those fields.  As a result, the overall net magnetic field of a given building is generally quite close to zero, and as a result a compass needs to be near enough to be affected by individual steel parts before there's enough effect to notice.
Install a magnetic compass in a steel hulled ship or a car, and you do need to "swing" the compass to null out the field of the steel surrounding it -- but this is because the compass is inside the steel.  Get even a few tens of meters outside the hull of that battleship, and the randomness of the fields of individual plates takes over and makes the overall field near zero -- not enough to affect a compass.

(I work on military ships) At least in the military world, many ships have degaussing systems to nullify magnetic signatures.

@RonBeyer I'd guess, however, that that's more about detection by an enemy than about making onboard magnetic compasses work better (especially in the modern GPS era).

Yes, that's right, but it does have that side effect.

The short answer is no, at least not to an extent that is noticeable or requires pilot compensation to deal with.
On the deck of an aircraft carrier with orders of magnitude more steel and signal density, the wet compass can be a bit squirrelly, but it goes away almost as soon as you are airborne.
Short duration approaches in the general proximity of a major city doesn’t have any noticeable effect.  While some effect may be measurable with sensitive enough equipment, it just isn’t an issue in practical terms.

I recall that Chicago had a particularly vexing magnetic disturbance off one of the runways that affected some airplanes, and required crews with AHRS equipped aircraft, where heading was coming from a flux valve, to take off in DG mode for the departure phase.  I don't know if it was ever determined to be man made or natural.  Concrete rebar has been known to cause problems locally.

@JohnK: Your comment jogged my memory of something I'd forgotten - KLGA has that problem too, courtesy of the steel framework used to hold the landfill that makes up much of the airport.


text:
Why doesn't the 737 MAX have an APU EGT gauge like all other 737s do?
On Original, Classic, and Next Generation 737s, the APU panel has an EGT (exhaust-gas temperature) gauge below the four APU caution/warning lights (all images in this question are from the 737 Technical Site).1
Original / early Classic APU panel (Garrett 85-129 APU):

Later Classic APU panel (Garrett 36-280 or Sundstrand APS-2000 APU; the NG uses the  Allied Signal 131-9(B), whose panel lacks the ammeter gauge but is otherwise identical):

In contrast, the 737 MAX, although it uses almost exactly the same APU as the NG (still the [now Honeywell] 131-9(B), just with minor bugfixes), lacks the NG's EGT gauge:

Given that knowledge of EGT is important for flightcrew awareness of an APU overheat or other malfunction, why was the EGT gauge removed from the MAX's APU panel?

1: Also visible in these two photos is the APU ammeter, present only on Originals and Classics.

@ymb1: I'm not seeing the APU panel anywhere in that picture you've linked to...

@ymb1: I see two lights there (not four), and the switches for the APU and engine generators, but not for the APU itself.

@ymb1: OH!

On the 747 the APU EGT gauge was removed with the -400 variant (which removed the FE position). Since the 757, no analog APU EGT gauge is installed anymore. The EGT can be seen on the EICAS Status page on these aircraft, but that display is not available when starting the APU without external power. Airbus actually installed analog APU gauges on the A310 maintenance panel (back of the cockpit) for this reason, but they are removed since the A320.

wait, @ymb1, the pics for the classic and NG had them photoshopped in? How bored do people get??

@FreeMan: No, the original/early Classic pic and the later-Classic pick (the question doesn't have a picture of the APU panel from an actual NG, but it's basically the later-Classic panel minus the APU ammeter) aren't photoshopped at all.  For the MAX, with the elimination of the APU EGT gauge, there are now no APU gauges needing that space below the four lights, and the space thus freed up became home to the rotary switch for the left windshield wipers.  Since the wipers are unrelated to the APU, said switch was photoshopped out of the MAX-APU-panel photo to remove extraneous detail.

Ahhh... gotcha. thanks for the clarification

You just never use that APU EGT gauge flying the NG. It’s almost pointless information as the APU ECU does it all. No non-normal checklists use it either.

Welcome to Aviation.SE! I removed your comment on MCAS since we try to keep answers on topic and free of opinion here.


text:
What safety issues led the FAA to ban Constellation flights into/out of the U.S.?
Although the Lockheed Constellation (like the other late, large piston airliners) was superseded in the 1960s and 1970s by newer jets (plus turboprops for shorter/lighter routes), it hung on into the 1990s with various Latin American airlines, who used them for international flights to and from the U.S.; this only ended in 1993, when the FAA abruptly banned the last of these airlines (all of them from the Dominican Republic, weirdly enough) from flying their Constellations in U.S. airspace.  According to Wikipedia, this ban was due to some sort of safety concerns:

Most Super Constellations were retired by their original operators after the advent of the Boeing 707 and Douglas DC-8 jet airliners. The last commercial flight of the L-1049 Super Constellation was in 1993, when the Federal Aviation Administration banned all airlines from the Dominican Republic that flew Constellations to the United States (due to safety concerns). The Dominican airlines were the last operators of any version of the Constellation.

I’m at a loss as to what those safety issues could be:

Was it due to concern about poor safety practices at those airlines, rather than concern about poor safety of the Constellation per se (but, then, why weren’t there at least one or two Constellation-flying carriers that did meet the FAA’s safety standards)?
The Constellation being an old, pressurised aircraft, were they worried about metal fatigue (but, then, why did the FAA impose a total flight ban on the Constellation, when fatigue-life concerns haven’t caused them to impose such a penalty on any other aircraft - especially since fatigue would be less of a concern with piston airliners like the Constellation than with jetliners, due to their lower cruising altitudes and resultant lower cabin pressure differentials)?
Were the old, large, temperamental multi-bank radials used by large piston airliners such as the Constellation simply incapable of meeting increasingly-strict engine-reliability requirements?
Was the FAA casting a jaundiced eye on the safety hazards of U.S. airports having to store vast quantities of the extremely-high-lead grades of avgas needed by the aforementioned engines?
Something else?

Weren't turbojets/turboprops declared the only approved 121ish airplanes?  Maybe the fact that they were piston airliners had something to do with the ban.

@acpilot: Got a source for that?

Nope, and I'm wrong.  Pt121 has provisions for piston aircraft.

Individual airlines, or even all of the airlines from entire countries, are sometimes banned for safety reasons. It was the Dominican airlines, not the aircraft, that were banned by the FAA.
It is just coincidence that many of these un-safe airlines flew Lockheed Constellations. They were banned from flying ANY aircraft into the USA.
The Wikipedia article talks about the end of Constellations used in commercial airline service, but it was the grounding of the airlines that caused the end, not the grounding of any particular aircraft.
Here is a link to a NY Times article describing a ban of all airlines from nine different countries.
Sept 3rd 1994 NY Times article

The Federal Aviation Administration has barred airlines from nine nations from flying to the United States because of poor safety procedures.
The unusual action, announced today, is a response to safety questions
  from consumer groups. Officials say they hope the economic fallout of
  the ban will encourage the airlines to follow safety guidelines.
The aviation agency surveyed safety procedures in 30 of the 93
  countries that have commercial flights to the United States. The
  agency sought to determine if the aviation authorities in each country
  were meeting the safety requirements of the International Civil
  Aviation Organization, a United Nations agency. Its rules are less
  strict than those of the Federal Aviation Administration.
The aviation agency did not reveal details about the safety
  deficiencies that had prompted it to ban the nine airlines.
The banned airlines are from Belize, the Dominican Republic, Gambia,
  Ghana, Honduras, Nicaragua, Paraguay, Uruguay and Zaire. Four other
  countries were allowed to continue flying into the United States, but
  under increased supervison by the aviation agency. They are Bolivia,
  El Salvador, Guatemala and the Netherlands Antilles.


text:
Are overwing exits still useable if the flaps can’t be lowered?
Essentially all narrowbody airliners (except for the very smallest propliners), and many widebodies as well,1 are equipped with one or more overwing exits for use in an emergency evacuation; these hatches, located at the window ends of rows of passenger seats, open (as the name suggests) onto the wing, from where, during a land evacuation,2 occupants escape off the trailing edge (almost never the leading edge, for some reason) in one of two ways:

On aircraft where the flaps reach within 6 feet of the ground when fully extended (the 737 is an example, as are most regional jets - DC-9, CRJ, etc.), the occupants simply slide down the extended flaps to the ground.
If the flaps don’t reach low enough on their own, as with widebodies, big narrowbodies, and the A320, one or more evacuation slides inflate from the exits over the trailing edge of the wing, providing a safe path down to the ground.

Either case presupposes that the aircraft’s flaps can be lowered completely; even if an aircraft has inflatable overwing slides, these are still designed to deploy over the lowered flaps (a slide designed to deploy over retracted flaps would trail on the ground with the flaps down, impeding egress from the bottom of the slide), while, with low-slung aircraft, the flaps are the slide.  However, many types of malfunctions can prevent an aircraft’s flaps from deploying fully, or at all:

A flap jam at a position other than fully-down will, obviously, prevent the flaps from deployed to the full-down position.
As flaps on essentially-all-but-the-smallest airliners are hydraulically-driven, a total hydraulic failure will render the flaps inoperable; on many-to-most airliners, even a loss of just one or two hydraulic systems will disable the flaps, as the flaps are less critical than the primary flight controls (the aircraft can still be safely landed with flaps retracted without much difficulty, while a safe landing with the primary flight controls inoperative is a crapshoot at best) and require a great deal of hydraulic force to deploy against the aerodynamic loads opposing their downward movement, making them a top candidate to be sacrificed if hydraulic-pressure-generating capability is limited (for instance, if all engines have flamed out and the hydraulics are running on RAT or battery power).

Do aircraft with overwing exits have special procedures for safely using the overwing exits in a land evacuation if the flaps can’t be lowered (or can only be lowered partway), or are the overwing exits simply unuseable on land if the flaps don’t deploy fully?

1: In some widebodies, the role of overwing exits is instead filled by full-size conventional exit doors a short distance forward and/or aft of the wing; these full-size exits allow for faster evacuation compared to the same number of overwing exits (which are limited in size by wing-root structural considerations), but create gaps in passenger seating, and, thus, are only used on aircraft large enough that the extra space required isn’t a problem.  Some widebodies, such as the 767, have both overwing exits and full-size near-wing exit doors.
2: In the event of a ditching, the water level typically comes all the way up to the wings, eliminating that particular problem (although creating several others).

The 737 doesn't have any special procedure for such a case. It would be the Captain's decision to use or not use the overwing exits. Factors such as the usability of other exits, the nature of the emergency, and the number of people on the aircraft would enter into the decision.


text:
Why are most of KBOS's instrument departures and arrivals jet-only?
I was looking through the big book o' KBOS instrument procedures when I noticed that almost all of the airport's SIDs and STARs are marked "NOTE: For turbojets only" or some variation thereof:

Of the ten instrument departures, nine (BLZZR Five, BRUWN Six, CELTK Six, HYLND Six, LBSTA Seven, PATSS Six, REVSS Five, SSOXS Six, and WYLYY Five) are jet-only, with only one (LOGAN Four) allowing non-jet aircraft.
Of the six instrument arrivals, four (JFUND Two, NORWICH Seven, OOSHN Five, and ROBUC Three) are jet-only, with only two (GARDNER Four and WOONS Two) available for non-jets.

Why are most of KBOS's instrument-departure and instrument-arrival procedures prohibited for non-jet aircraft?

What kind of traffic does the airport serve?

KBOS = Boston Logan International Airport

Performance.
And the fact that most of their traffic is jets.
The difference is, "jets" are pretty much all capable of accelerating quickly to 250 knots and climbing out expeditiously, and flying 250 knots until you want them to slow down on an arrival, and the design and use of these procedures works on the assumption that the traffic on them can all do this.
Having separate procedures for the non-jets ensures that you don't end up with a slower, lower-performing aircraft "clogging up the pipeline" -- they are assigned different procedures with different routes.
If the airport had a more equal mix of props and jets, you might see a more balanced ratio: a "jets" departure heading north, a non-jets departure heading north; a jets departure heading south, etc.  But since Logan has comparatively few non-jet departures (not zero; Cape Air has some presence there), it's probably easiest just to have the props all get a single departure consisting mostly of radar vectors, and have the controllers get them pointed where they want to go while keeping them clear of the arrival/departure corridors in use.  As opposed to designing a bunch of routes to accomplish that, which wouldn't be used all that often, as would be necessary if you had as many props-north / props-south / etc procedures as the jets do.


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Why can’t more older 737s be retrofitted with more newer winglets?
Some background: there are four different types of winglet that have been used on various 737s over the years.

The mini winglet is used to retrofit 737-200s (one of the two 737 Original variants, the other being the 737-100).  It is basically a tiny trapezoidal tab riveted to the rear portion of the wingtip.

(Image by Julian Whitelaw at airliners.net, via meisam nemati here at AvSE.)

The blended winglet is what most people think of when they hear the word “winglet” - an attachment that looks like someone simply extended the wingtip and then bent it up to near-vertical.  It was factory-installed on all 737 Next Generation variants (the 737-600/-700/-800/-900) for the first two decades of production, and has also been retrofitted on most of the 737 Classic models (the 737-300/-400/-500) that remain in service.

(Image by Ralf Roletschek at Fahrradtechnik auf fahrradmonteur.de via Wikimedia Commons, modified by Altair78 at Wikimedia Commons.)

The split-scimitar winglet has replaced the blended winglet on the last few years of the Next Generation production line; it is shaped somewhat like the blended winglet, but a) is swooshed rearwards at its upper tip, as opposed to the simple trapezoidal tip of the blended winglet, and b) has an additional scimitar-shaped, rearward-swept fin projecting from the outside of the upbend in the winglet.

(Image by Mnts at Wikimedia Commons.)

The MAX winglet is used on the 737 MAX series (737 MAX 7/8/9/10); it, too, is a split winglet,1 but of a simpler shape than the split-scimitar winglet, looking much like someone extended the wingtip outwards, then split its upper and lower surfaces away from each other and bent them upwards and downwards, respectively, to form what looks remarkably like a glorified Airbus wingtip fence.

(Image by Aka The Beav at Flickr, via Helmy oved at Wikimedia Commons, modified by Altair78 at Wikimedia Commons.)
Now for what I’m curious about:

Although the 737-100 (the original Original) was produced in smaller numbers than the 737-200 and is no longer in service, it still hung on with various operators past the turn of the millennium; why weren’t any -100s also retrofitted with mini winglets, given that the -200 is basically just a stretched -100 with more fuel capacity?
Given that the blended winglet, despite being originally designed for the Next Generation wing, was retrofitted on the vast majority of the Classic fleet with little to no trouble, why couldn’t it also be retrofitted on the remaining Originals, given that the Classics are essentially CFM56-engined, (sometimes) stretched -200s?
Seeing as the Next-Generation-designed blended winglet was easily adopted for the earlier Classics, what keeps the split-scimitar winglet, likewise designed for the Next Generation wing, from also being retrofitted to the Classics?

(Yes, I know that this is three questions rather than one, but I felt it was better to have one question asking three closely-related questions than to clutter up the homepage with three separate but near-identical questions.)

1: As for why Boeing went to the trouble of developing two different styles of split winglet for the two in-production 737 families, that’s a different question.

The 737-200 mini winglets was certified in 2005. How many -100s flying in 2005 ? BTW, actually, only one -200 was equipped through the program, and it is rumored that it never flew. The picture depicts a mock-up demonstrator (no structural modification to the wing tip, not enough rivets to hold the winglet inflight - and the nav lights are missing)

737 Classics : 100 and 200 or "originals" with PW JT8D. 300, 400 and 500 or "glass cockpit" with CFM56. Both have slightly different wings and wing structure, different spoilers, different flaps, different engine thrust. => very different mechanics,  aerodynamics and loads. Everything outboard the landing gears has been revised. Blended Winglets certification for the originals would have been very time consuming. BTW, retrofit on classics... "Eyebrows retrofit", yes, winglets, not that vast. And no -400 as far as I know got winglets. It's not just a matter of stretching the -200 ;)

Split Scimitar has two sails, one pointing downard. Ground clearance is not enough on hypothetical retrofitted classics where wingtips are closer to the ground compared to NG and Max. BTW, that will slightly increase wingspan, some airlines (operating on some airports) may refuse to invest in the retrofit to avoid wingtip strikes incidents. Certification is the same story as above.

In order to develop and test a new product, you have to be sure that there is a sufficient market for it. Because of how aircraft certification is handled, it doesn't make sense to test a modification for a model that can't sell enough units to pay for itself.
As you noted, the 737-100 is the most extreme example, where only 30 of the 737-100 were ever built, and the 737-200 saw over 1000. This gave them a market roughly 30 times larger. It probably didn't make sense to certify the mini-winglets on the 737-100 if there were only a handful of airplanes that would use it.
By the time the makers of the blended winglet were ready to look at derivatives, the mini-winglet was already available, or soon would be. The development cost may not have supported splitting the market, especially since the mini-winglet was part of a more extensive flap modification that provided other benefits.
As for the split scimitar, while airlines have seen the benefit of retrofitting it to the relatively new NG line, they may see less benefit of putting on the older classic line, especially if they are still trying to reach the payoff for paying to put the blended winglets on.

Why not combine the blended winglet with the flap modifications from the mini winglet programme?

Winglets change the spanwise loading on the wing. By increasing the effective span of the wing, lift is increased towards the tips of the wing. With more lift there, you get an increased bending moment on the wing.
All this means is that you can't just put winglets on or change the ones you have. You must retrofit the structure of the wing which is very expensive and requires significant downtime. It also adds a weight penalty which decreases the benefits of the winglet.
For example, on the A320, which was already wingtip fence equipped, going to the sharklets requires removing the skin and reinforcing both the tip and the center wing box near the fuselage. This takes the aircraft out of service for 15 days and involves, I've heard, in excess of $1 Million in parts alone.
On the 737, the list price for the blended winglets is $1.06 Million.
So the answer for why is because it often is not economical to do such a huge modification given the limited lifetimes on older models.

"So the answer for why is because it often is not economical to do such a huge modification given the limited lifetimes on older models."  ...even when you factor in the considerable lifetime extension that could be gained by reducing their fuel burn (given that jetliners are generally replaced when they become uneconomical to operate, and usually long before the aircraft actually reaches its fatigue-imposed life limit)?

Because there is not much point.
Winglet increases effective wing span. It is not as good as just increasing the span, but it is simpler to redesign a shorter wing by adding winglet than designing a longer wing, and keeping the wingspan down is useful so the new version can still usie all stands and taxiways the previous version could.
However, if the aircraft was designed with appropriate span for its weight and cruise speed, increasing the span is not what you want. While it would decrease the drag at the best lift/drag point, it would push that point to lower speed, and the drag at the original cruise speed would increase.
Winglets are added to the newer versions, because they are also given more powerful engines, which allow higher take-off mass. The higher weight requires more lift, which increases the best lift/drag speed, so increasing the span is needed to compensate. And modifying the wing by adding winglets is much easier than making it larger, because while it may still need strengthening the spars, as the bending moments do increase, all the other systems like flaps and ailerons and deicing and fuel system can stay the same.


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When and why was runway 07/25 at Kai Tak removed?
Wikipedia states that Kai Tak Airport in Hong Kong originally had two runways, both built under Japanese occupation during World War II:

... In 1942, the Japanese army expanded Kai Tak, using many Allied prisoner-of-war (POW) labourers,[9] building two concrete runways, 13/31 and 07/25.

However, by the time Kai Tak was closed in 1998, only one runway (the famous 13/31) remained.  I can find no mention of when runway 07/25 was closed, or why; can someone help answer those questions?

Because @Terry told them it was of no use as he could not land his 747 there...


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Why did KJFK keep using runways 22R/L here instead of switching to 13R/L?
In this YouTube video, one can see the arrival at KJFK, holding patterns, and eventual diversion to KPHL of LH400, an A380.  When LH400 arrives in the New York area, the pilots request the use of runway 13R, the longest runway at the airport, since, with the runways wet from bad weather, their aircraft is too heavy to safely use any of the others, and the winds (from headings in the 100-130 range, at 15 knots gusting to 28 or so) are better aligned with runways 13R/L than with any of the other runways.
However, KJFK is operating with runways 22R/L, and the approach controller refuses to switch to 13 ops to allow the A380 to land.  Part of the justification given for this is that the bad weather had also shut down KTEB, causing KJFK to experience a large wave of corporate and private aircraft diverting from KTEB, and that switching from 22 ops to 13 ops for LH400, and then back to 22 ops, would have massively delayed the landings of the general-aviation flock.  Without enough fuel to wait out the wave of aircraft coming in on 22R/L, LH400 is forced to divert, and lands safely at KPHL.
With winds from 100-130, though, using 22R/L rather than 13R/L seems illogical (especially given the presence of an aircraft unable to land on either 22R or 22L).  Winds from the southeast to east-southeast would produce a quartering or even straight headwind for 13R/L, but a crosswind or quartering tailwind (even worse for aircraft than a crosswind!) for 22R/L; in addition, while the 4/22 runways measure 8,400 and 12,079 feet in length, the 13/31 runways measure 10,000 and 14,511 feet.  The choice of 22R/L is especially hard to understand when you find out that the winds had been like this all day, making one wonder why they even started 22 ops that day in the first place.  Even with 22 ops already in operation, one would think that the time needed to switch over to 13 ops would be more than justified by the safety benefits of landing aircraft on longer runways facing more nearly into the wind (especially when, as here, aircraft will be needing more landing distance than normal, due to reduced wheelbrake effectiveness on contaminated runways).
Why did KJFK run 22 ops that day when the winds favored 13 ops, and why didn't they switch to 13 ops even when confronted with an aircraft unable to take anything but 13R?

This question deals with changing runway use: https://aviation.stackexchange.com/questions/9126/how-does-a-large-airport-switch-flow

This boils down to a question of traffic flow coordination in a terminal area.

@StephenS: Still doesn't answer why the frick they were using 22 ops in the first place.

Due to close proximity, the runways in use at JFK, LGA and EWR must be carefully coordinated to maximize total volume.
In particular, instrument approaches to JFK on the 13s and departures off the 31s all go over LGA. Plus, arrivals on the 4s and departures off the 22s all go over EWR. So, there is a very strong preference for JFK using 4s or 13s for departures and 22s or 31s for arrivals, regardless of the winds. And all the diversions from TEB would have made it even more important to stay that way.
If the crosswind or tailwind on the preferred runways gets so bad that most aircraft will have to refuse their assignment, ATC will change things—and they know exactly where that line is. But to maintain safety with conflicting approaches and departures requires more spacing between planes, which directly results in lower total capacity. Many flights will get delayed, diverted or canceled, and the problems will cascade across the entire US airline system. This obviously has an enormous cost, both to the airlines and to passengers, so ATC will run things right up to that line for as long as possible.
It’s simply not worth paying that cost for the sake of one aircraft; instead, they’ll get diverted to another airport with more favorable winds.


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When are winglets most effective?
If winglets reduce induced drag, induced drag is greatest at slow speeds. When are winglets most effictive?

Possible duplicate of Is wingtip design mature?

At low speeds.  This is why you see them on jet airliners, which cruise a low "indicated" airspeeds, just low enough that the vortice strength is enough to get a decent lift vector out of the winglet from the flow.  An airliner cruising at M.78 say, at FL380, is only going about 2x its flaps up stall speed.  A straight wing airplane at 20000 ft cruising at 250 kt might be going 2 1/2 to 3x its flaps up stall.  The vortices aren't strong enough in that case and you see them on straight wing airplanes rarely, and if you do it'll be to improve rate of climb more than anything, or maybe simply "styling".


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Can a surrendered type certificate be reacquired by the manufacturer or by another entity, or is it considered to be permanently lost?
On occasion, the holder of an aircraft type certificate or supplemental type certificate chooses to surrender it to its local civil aviation authority (for instance, the FAA or EASA), which has the effect of grounding all aircraft covered by the type certificate; can the former holder, or another person or entity, later reacquire the surrendered certificate, or is a surrendered type certificate permanently voided?

From the FAA point of view, the TC is not lost but cannot be reissued. You have to get a new one if you want to become the new TC owner. Order 8110.120 states:
"The surrender of a certificate is a final action. Once surrendered, the action cannot be reversed. A certificate cannot be reissued to a third party or a former holder. A new TC for the product could only be issued as part of the full TC process with a new application, subject to all current regulations."
I don't know EASA's policy but I suspect it likely mirrors the FAA's.
In addition, your statement that aircraft covered by the surrendered TC are grounded is incorrect. Surrendering a TC does not affect the airworthiness status of aircraft produced under the TC. From the same document linked above:
"The surrender of a TC does not affect the airworthiness certificates of existing aircraft. The aircraft remain subject to future AD actions for safety of flight issues that could affect their airworthiness certificates."


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What are these hexagonal things under the Concorde's neck?
The Concorde had a pair of dark-coloured hexagons under each of its forward boarding doors, as seen in this picture (showing the hexagons on the left side of the Concorde's neck):

British Airways Concorde, Pictured by LondonAirTravel at the BA Engineering Base, London Heathrow (link)
What are they, and what purpose do they serve?  They obviously aren't passenger or crew windows, and they're far too big to be static ports yet far too small to be cargo doors - some sort of maintenance access panel, maybe?

Here is a link to a better picture: https://i2.wp.com/londonairtravel.com/wp-content/uploads/2017/01/concorde01.jpg

(source)

This is the side loading door. Under this door are the static pressure
  panels that provide data to the Air Data Computers. They have been
  painted over now.

Here is a nice close up image

(source)

I think the first image you posted is the opposite side of the aircraft that these are on, I don't think they were painted over (at least not on the right side). The second image seems to be missing the lower door you see in the first one.

The first picture looks like it has the covers installed or possibly the original components have been removed and stored and a replacement panel affixed. More like the second option as covers would be brightly marked and/or flagged 'removed before flight'.

@RonBeyer I would imagine there were redundant sensors on either side of the aircraft as is typically the case. Im also not sure if the first and second picture are of the same airframe.

So I was half right; they are much too big to be the static ports themselves - but not too big to be the panels that the static ports are mounted on!


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Why doesn’t the A320 have any provision for manual aileron trim?
To eliminate the need for pilots (human or automatic) to maintain continuous force on their aircrafts’ yoke/joystick and rudder pedals while flying, aircraft generally have some sort of trim mechanism for each of their three rotational axes.  The underlying operating mechanisms vary,1 but, from the pilots’ perspectives, they adjust the trim so that it takes up the forces that the pilots would otherwise need to apply to the aircraft to maintain its desired attitude.  (For instance, if a pilot has to hold continuous nose-up pressure to hold attitude while slowing to land, they can dial in nose-up trim until the aircraft’s pitch remains steady even if they let go of the yoke or joystick; if they have to continuously hold down the right rudder pedal to counteract the yawing moment from a left-engine failure, they can dial in right rudder trim until they no longer have to stand on the pedal; and, if they have to turn the yoke [or tilt the joystick] and hold it in this position to compensate for a fuel imbalance or flap/slat/spoiler/whatevs asymmetry, they can dial in left/right-wing-down aileron trim until the aircraft no longer rolls one way or the other with the yoke or joystick released.)
Aircraft generally have, for each rotational axis, one or more sets of wheels or switches to allow a human pilot(s) to manually adjust the trim in the desired axis; additionally, most autopilot-equipped aircraft possess the ability to automatically trim the aircraft in at least the pitch and roll axes (and frequently the yaw axis as well), a feature known, unimaginatively, as autotrim.  For pitch trim (the one a human pilot will have to adjust most frequently, by quite a wide margin, as well as, for almost-all larger-than-small aircraft, the only axis in which the control authority of the trim system exceeds that of the aircraft’s primary flight controls [and, thus, the only axis about which an unchecked trim runaway is capable of generating rotational moments that cannot be countered simply by manipulating the primary flight controls]), there are generally two or three redundant sets of trim controls (two electrical trim-adjustment mechanisms - one on the yoke or joystick, for easy, immediate access while flying the plane, and one on the instrument panel or center console - plus usually a pair of backup manual trim wheels next to the pilots’ inboard thighs).  Roll and yaw trim, in contrast, are used much less often and have less potential for catastrophe in the event of a trim runaway that can’t be stopped manually, so they can usually get by with just one manual-operation mechanism each, usually a thumbwheel or pair of more-left/more-right switches; even so, however, the vast majority of aircraft do have at least some means for a human pilot to adjust rudder or aileron trim.
Enter the A320, which apparently has no provision for allowing a human pilot to retrim the ailerons:

Cockpit Controls
Each pilot has a side-stick controller with which to exercise manual control of pitch and roll.  These are on their respective lateral consoles.  The two side-stick controllers are not coupled mechanically, and they send separate sets of electronic signals to the flight control computers.  Two pairs of pedals, which are rigidly interconnected, give the pilots mechanical control of the rudder.
The pilots use mechanically interconnected hand wheels on each side of the centre pedestal to control the trimmable horizontal stabilizer.
The pilots use a single control on the centre pedestal to set the rudder trim.  There is no manual switch for trimming the ailerons. [National Transportation Safety Committee Aircraft Accident Investigation Report KNKT.14.12.29.04, page 30 (page 32 of the PDF file of the report).  Header text bolded in original; other emphasis mine.]

This seems like a pretty dodgy design decision - in the event of an aileron-autotrim runaway, or of an aileron-autotrim failure combined with anything that would impart a large rolling moment to the aircraft (for instance, a fuel leak draining fuel from one wing, or an asymmetric-flap-or-spoiler situation), a human pilot would have to haul the joystick over to oppose the resultant roll, and hold it there, without any ability to trim out the rolling moment and recenter the joystick, for as long as the rolling-moment-inducing situation lasted (all with one hand, mind you, since Airbus place their joysticks way off to the side where a pilot can only use their outboard hand to manipulate them), while also making any necessary pitch inputs at the same time with the same joystick, likely resulting in heavy cross-coupling between pitch and roll, what with the pilot trying, all with one hand, to maintain a steady lateral roll input while simultaneously pushing and pulling the joystick forwards and back to make pitch inputs.  Why doesn’t the A320 allow its human pilots to trim its ailerons?

1: For roll and yaw trim, plus pitch trim on most small aircraft, this usually takes the form of some sort of mechanism that adjusts the neutral position of the control surface(s) in question, typically either (for aircraft with fully-mechanical flight controls) by adjusting control-surface-mounted trim tabs (which, when deflected, create an aerodynamic force that causes the control surface in question, instead of returning to its faired position when the cockpit controls are released, to seek out a position a greater or lesser distance away from the faired position),2,3 or (for aircraft with hydraulic or electrohydraulic flight controls) by biasing the aircraft’s artificial-feels mechanism to make the relevant control-surface actuators apply a continuous force of the desired magnitude and direction.  On most midsize-and-larger aircraft, pitch trim works by adjusting the angle of incidence of the aircraft’s horizontal stabiliser; the much-greater area of the horizontal stabiliser compared to the elevators greatly increases the aircraft’s maximum pitch-trim authority (allowing the aircraft to be trimmed for stick-free flight throughout much greater ranges of airspeeds and center-of-mass positions, but making a pitch-trim runaway potentially far more serious - a severe pitch-trim runaway in an aircraft with a trimmable horizontal stabiliser can easily generate a pitching moment in excess of the elevators’ maximum ability to counter) and requires much less deflection for a given trim input than the elevators would (reducing drag), while, as the elevators are mounted to the horizontal stabiliser, and move with it, elevator and pitch-trim inputs stack on top of each other, instead of pitch-trim inputs being taken out of the available elevator authority (as is the case for aircraft using the elevators for pitch trim).  A few aircraft use fuel transfer or pumpable water ballast to move the aircraft’s center of mass forwards or aft for pitch trim, removing the need to move the elevators or stabilisers at all, but making large trim changes using this method requires the carriage of a correspondingly-large mass and weight of trim fuel or water ballast (although it can still be quite useful in reducing trim drag midflight, while the aircraft still has quite a lot of fuel left).
2: On many aircraft, these tabs are also used to move the control surfaces in response to flight-control inputs; when operating in this function, they are known as servo tabs.  Most larger aircraft with manually-operated or manually-operable flight controls have servo tabs (even ones that don’t use tabs for trim), as they greatly reduce the required control forces in manual flight (compared to if the pilot(s) had to haul around the big primary control surfaces directly).
3: Some aircraft have trim tabs that are not mounted to the aircraft’s primary flight-control surfaces, but, rather, directly to the aircraft’s immovable structure; instead of trimming the aircraft by adjusting the positions of the primary control surfaces, these act as an additional slow-moving elevator/aileron/rudder/whatnot whose deflection can be varied to adjust the total rolling/pitching/yawing torque on the aircraft.

Pretty sure the FBW system takes care of it in the background.  The biggest function of aileron trim is fixing minor rolls because the rigging isn't right on or a wing plank has a bit of twist. A given airplane will generally need the same aileron trim input all the time.

The normal flight law behaves as if it auto-trims the aileron, but there is no actual trim involved. The computer simply derives the desired deflection of ailerons using the pilot input and feedback from the inertial reference system. So

In normal law (which requires working inertial reference) neutral side-stick means maintain bank angle, so effectively auto-trim.
In alternate and direct law (after various failures; mostly multiple failures required) neutral side-stick means neutral ailerons. They don't have anything to add bias to them, only the hydraulic actuators, so the risk that significant deflection is needed to maintain wings level is extremely improbable. Some periodic adjustment might be needed though. It only happens upon multiple failures and you are probably trying to land ASAP anyway.
In mechanical backup the ailerons are not active at all (not sure whether they stay neutral or even float free) and yaw-to-roll coupling is used. Mechanical backup is only used after many things have failed. There was one accident where it was needed, and the aircraft was controllable enough that while it did get damaged on landing, nobody was hurt.

It is different from elevator, where there is a trimmable horizontal stabilizer that does maintain position without any command, so the trim wheels for that are essential. And from rudder, which has mechanical link (for sake of the mechanical backup), so needs a mechanical trim as well.
The yaw-to-roll coupling also means that some tendency to bank can be trimmed away by adding a bit of side-slip with rudder trim.

In alternate law lateral control is direct for the A320. You need constant adjustments to keep the aircraft wings level.

@AnasMaaz you are right; I misremembered that part. It's a bit strange though; the inertial reference, specifically vertical acceleration, is still used for the pitch control, so it seems strange to stop using roll rate for roll control.

There is no need for aileron trim because the flight control system keeps the bank angle constant if there is no lateral input on the side stick. The pilots use the side stick to roll the aircraft to the desired bank angle and then hold the stick neutral. The FCS will then maintain that bank angle by giving the right amount of aileron input. The exception is that if an extreme bank angle is commanded (> 33°), the FCS will reduce that bank angle to 33° and then maintain it.
From the same accident report:

Lateral Control
When the PF performs a lateral input on the sidestick,
a roll rate is ordered and naturally obtained. Therefore, at a bank
angle of less than 33°, with no input on the sidestick, a zero roll
rate is ordered, and the current bank angle is maintained.
Consequently, the aircraft is laterally stable, and no aileron trim is
required.

Source: National Transportation Safety Committee Aircraft Accident Investigation Report KNKT.14.12.29.04

Airplanes are designed with less lateral stability when compared to longitudinal stability and directional stability. This means, they are very nimble and easy to control in the roll axis. If you have flown any aircraft you will realise that it is way easier to roll an aircraft than pitch it up and down. A longitudinally unstable aircraft can easily go out of control. Imagine a disturbance pitching up an aircraft. If it has less longitudinal stability it will continue to pitch up and may cause a stall. The pilot will struggle to control the pitch up as the reduced stability will make it harder to keep it from pitching up. An aircraft which has less lateral stability is easier to manage. It does not have consequences such as increased load factor on the air frame and it cannot stall an aircraft either. Because longitudinal stability is high you need trimming, to keep the aircraft's own stability from preventing a pilot desired maneuver. Roll stability is comparatively low, so a pilot can control it with little to no trim.
In large aircraft, aileron trim is not used in normal flying 99% of the times. I flew the Dash 8s and it had an aileron trim and even when we hand flew the aircraft, I have not seen anyone messing up with the aileron trim. If the control cables are set correctly, the aircraft is extremely easy on the hands. Even in engine failure situations, you do not require the used of aileron trim. The Dash 8s have a strong tendency to roll towards the failed engine. You could use the aileron trim, to trim this out but it is easier to counteract this without any trim at all, as power changes during the flight and particularly in approach requires too much re-trimming.
You also asked about a trim runaway. In a trim runway, you want to disable the trim it self. Again, in the Dash 8 if we have an aileron or a rudder trim runway, the pilot flying will use the yoke to wings level the aircraft and the pilot monitoring have to use the trim switch to center the trim and at the same time find the circuit breaker for the trim and pull it. As the aircraft has an electrically operated trimmer, this will immediately shut it off. There is a special QRH procedure for it.
Now, let us talk about Airbus. Modern Airbus aircraft in normal law have automatic trim in pitch and roll axis. In A320, if the aircraft control laws degrade to alternate law, the roll control becomes a direct stick to control surface relationship. As with other aircraft, the roll control in direct is very easy to control in the A320. You have mentioned about a fuel leak causing an imbalance in the tanks which can tire a pilot. It is most certainly possible for an imbalance to occur. But such an imbalance would not result in extreme rolling moments which are harder to manage. Neither will flap or a spoiler asymmetry. And keep in mind that use of aileron trim will always cause the control column has to be physically deflected to maintain the aircraft wings level. This is not what exactly we want. You do not want to land an aircraft with a deflected yoke or stick. If you need to continuously deflect the control column, be it a yoke or a side stick. The better way to do this will be to introduce a little side slip by the use of rudder trim. There is a procedure which requires this in A320. When the aircraft suffers from a Green + Yellow  hydraulic system failure, the right aileron momentarily is not powered because a) Green hydraulic power is gone and b) The ELAC 2, the computer which powers one of the right aileron actuators is shed. This will move the right aileron into its zero hinge moment position. In this position, there is an aileron up float which can cause a rolling moment. Airbus recommends to use rudder trim in this situation so that you do not need to apply a constant side stick deflection to keep the aircraft wings level. The application of the left rudder will increase the speed of air flow over the right wing, which will increase the lift over the wing and the aircraft will go wings level.

For a fuel imbalance situation, again the aircraft is flight tested to fly with one full wing tank and one empty wing tank to the landing.


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Why is the 707’s yaw-damper-out lateral controllability marginal to nonexistent with flaps and spoilers extended?
According to the NTSB report on the 1973 crash of Pan Am Flight 160, the 707-300C1 has lateral controllability characteristics ranging from “minimal” to “none” if the flaps and spoilers are extended with the yaw damper inoperative:

Performance data for the Boeing 707-321C[2] show that lateral control capability may be extremely limited, if not impossible, with an inoperative yaw damper, extended spoilers, and lowered flaps.  [NTSB-AAR-74-16, p. 31 (marked as 29).]

On most aircraft, the yaw damper, although useful, can still be rendered inoperative in all flight regimes without causing the aircraft to become uncontrollable.  Which makes sense - of the two main uses for the yaw damper (minimising Dutch roll and helping to counter adverse yaw), the first is of little consequence at the low altitudes where the flaps and spoilers are most likely to be deployed simultaneously (as Dutch roll is strongly damped out by the thick, dense low-altitude air), and is not generally a threat to controllability even when weakly damped at high altitude3 (although it excels at making the aircraft’s occupants airsick), while adverse yaw can be countered just as well by manual rudder inputs (something every jetliner pilot will have long since learned how to do, manual rudder usage being necessary for making coordinated turns in the small general-aviation planes pilots first learn to fly in) as by the yaw damper.  Granted, the very high induced drag generated by flap and spoiler deployment (mostly the latter) would considerably aggravate the aircraft’s adverse-yaw tendency,4 but, assuming that the 707’s rudder was adequately sized to begin with, the aircraft should still remain completely controllable with the proper manual rudder inputs.
Indeed, if the 707-300C (and possibly the other variants as well) is truly uncontrollable in the lateral axis, or almost so, with flaps and spoilers deployed and the yaw damper inoperative, it is somewhat difficult to see how the aircraft could ever be safely flown without a functional yaw damper; takeoff and cruise wouldn’t pose too much of a problem, but landing, as a rule, involves a considerable amount of flap due to the resultant decrease in landing speeds, with spoiler extension being used to slow the aircraft down during the descent, and, if the yaw damper is indeed necessary for the 707(-300C) to be controllable with flaps and spoilers extended, one would expect a loss of control at some point during the descent/approach/landing sequence if it were flown without an operative yaw damper.
Why is the 707 so difficult to control with the yaw damper inoperative and flaps and spoilers extended?

1: The 707-300C was the most-produced civilian 707 variant; the other variants (-100, -100B, -200, -300, -300B, and -400), which differed mainly in fuselage length and engine selection, presumably behave similarly to the 707-300C for the purposes of this question.
2: A Boeing 707-300C built for Pan Am (Boeing customer code *21).
3: I am aware of only one case where Dutch roll actually caused an accident (and the aircraft still would not have crashed were it not for a generous heaping of pilot error).  This was a 707-200 training flight in 1959, conducted with the yaw damper off, where the aircraft’s motions were greatly amplified by improper and excessive flight-control inputs by the pilots, causing a loss of control; the aircraft was eventually recovered from an inverted dive, but three of the four engines were torn off at some point in the process, and the aircraft crashed short of an intended emergency-landing site when flight-control damage from the resulting fire forced the remaining engine to be throttled down in order to maintain control.
4: Flap deployment increases the induced drag of the wings directly; however, this should not, on its own, cause a large increase in adverse-yaw tendency, as the flaps are located on the inboard portions of the wings (there being more room for them and their associated paraphernalia in the wide, thick wing roots than nearer the thin, narrow tips, and there being less additional wing-bending moment if the increased lift from the flaps is added as close to the fuselage as possible), while the ailerons (the increased induced drag from the downward deflection of which is the cause of adverse yaw) are located on the outer, unflapped portions of the wings, as far from the aircraft’s centerline as possible, in order to achieve the maximum possible roll control authority.5  Spoiler deployment increases the wings’ induced drag indirectly, by forcing the aircraft as a whole - including the ailerons - to fly at a higher angle of attack in order to maintain flight, causing an increase in adverse yaw.
5: Indeed, flap deployment could (depending on the aircraft and the exact flight conditions) even help in this regard, as the increased lift from the deployed flaps allows the aircraft as a whole to fly at a lower angle of attack, reducing the aircraft’s adverse-yaw tendency; the 737, a later Boeing aircraft, shows an example of this.

As airspeed decreases, DR damping becomes increasingly worse.

Dutch roll is rolling, yawing and pitching together in a sort of Lazy 8-like pattern, and if divergent or really severe, there are very few humans that can make the perfectly timed in-phase inputs required to not make the motions worse, without a lot of advance training to get the pilot inside the response loop, which nobody does, so it's not a case of bad piloting when an airplane crashes due to a dutch roll event.
Since DR is related to the very powerful roll/yaw coupling of swept wing airplanes, the coupling is worse flaps down than flaps up, as the flapped wing presented straighter into the airflow by the yaw gets an even bigger lift boost compared to the trailing wing than with flaps up; it wants to roll even harder at the same yaw angle and speed (you learn this pretty fast the first time you do an engine cut simulation on a full flap go around and are late with the rudder). On top of all that what natural yaw damping there is, is reduced by the lowered airspeed.
I believe that most swept wing airplanes with dutch roll tendencies are worse flaps down than flaps up, although not necessarily bad enough to become uncontrollable.  I know that the CRJ Regional Jet line has a stable dutch roll mode flaps up (you can excite a DR and if you do nothing it will settle down by itself... eventually) but is mildly unstable flaps down, although this isn't bad enough to prevent it from being dispatchable for 10 days with a Y/D channel inop with no restrictions (one channel working, and failure of that is not considered an excessive risk over a 10 day exposure period).  Other aircraft may have MELs that allow single Y/D channel operation only with a flap extension restriction. It would be interesting to see what the 707's MEL says.
Also, adverse yaw is just one potential excitation mode. Turbulence can also excite a yawing motion that can get a dutch roll going and is probably a bigger one than AY.
In the case of the 707, its dutch roll mode flaps down was clearly divergent and severe enough to be considered uncontrollable by a normal pilot, and I'm pretty sure it's not the only one.

Yeah, about the only pilots that were trained for dutch roll control to a decent level of proficiency were USAF folks who had to deal with the old KC-135As and their combo of marginal native dutch roll stability and lack of yaw damper hardware to compensate for that marginal native dutch roll stability...

Why is the 707 so difficult to control with the yaw damper inoperative and flaps and spoilers extended?

It is a matter of time constants and stability of responses:

Stable responses return to equilibrium position after a disturbance. As in a damped $2^{nd}$ order response. The amount of damping determines the number of overshoots before returning to equilibrium.
A neutral response continues to sway indefinitely after a disturbance, at constant amplitude and time period. There is no damping.
An unstable response sways with diverging amplitude away from equilibrium. There is negative damping.

An active controller, such as a pilot behind the flying controls, can generate control inputs that return an uncontrolled response to equilibrium more rapidly. How easy it is for them to do that, depends on the amount of damping in the system itself: too much damping, and their inputs must help the system to return faster. Too little damping, and they must counteract what the system does - but the systems oscillates, so their inputs must oscillate as well.
Humans, like all control systems, have a certain time delay between sensing a motion and being able to generate an effective control input. If the sway period is too rapid, this time delay causes the input to come at a time where it does not counteract the motion. To an extent, humans can learn how to time and dose their inputs in order to control an unstable system, if the time period is long enough - a helicopter in the hover is a classic example.

...it is somewhat difficult to see how the aircraft could ever be safely flown without a functional yaw damper;

Landing without yaw damper is possible if the spoilers are not used.
Landing without using the spoilers is possible on a stable approach.

It's just that the pilots need to know that the yaw damper is inoperative and that therefore the time constant of their responses must be adapted. Whether they are trained to do so in that particular situation is a different matter...

While each aircraft is different, especially for ones with high amount of sweep, some general trends can still be predicted:

The Dutch-roll damping decreases with decreasing speed (Ref. Etkins, Dynamics of Flight, Wikipedia).
Increasing flap increases the dihedral effect (Ref. ESDU 80034), which worsens the Dutch-roll damping once again (Ref. Etkins, Dynamics of Flight, Wikipedia).

MIL-STD-1797B specification recommends at least a damping ratio of at least 0.02 for all phases of flight for a Handling Quality Level 2, which is often the minimum threshold for a landing task (Level 3 is the minimum for continued safe flight). If the Dutch-roll damping falls too low, it can certainly be dangerous.


text:
Why do windowless cargo Metroliners still have overwing-exit hatches?
One of the variants of the Metroliner, the SA227-AT Expediter, is a dedicated cargo aircraft with strengthened floors, an increased MTOW, and a windowless cabin.
However, despite being a cargo aircraft with absolutely no provision for the carriage of passengers, it appears, bizarrely, to still have been built with hatches for overwing exits!

(Image by YSSYguy at Wikipedia, via YSSYguy at Wikimedia Commons.)
Why are these hatches still included when there are no passengers to evacuate through them and cutting them into the aircraft's hull weakens its overall structure and requires extra time and labor during construction?

Might come in handy for the loading crew should a fire break out while on the ground.

The window openings are still there, they are just filled with aluminum panels replacing the acrylic ones, and the joints are fine enough they don't show up in pictures unless the light is coming at low angle to the surface like in the shot below.
Nobody would ever build a cargo conversion of a passenger aircraft (as opposed to designing the fuselage of a special cargo variant of a passenger jet model from scratch) and go to the trouble of designing a completely new fuselage barrel to just to eliminate the window frames.

In this picture you can see some of the window frames on the exact aircraft from the question (VH-EEO). Does your last sentence also apply to big cargo jets? I always thought that purpose built freighters like the Boeing 777-200F do not have window frames (unless they are converted passenger planes).

My answer is about converted pax planes. It makes sense that they would eliminate windows, as well as building in a large cargo door, during design on a dedicated freighter model.

This answer could use some clarity. When you say "build a cargo conversion" do you mean a new-build freighter from a passenger design (777-200F) or a conversion from an existing passenger airframe (P2F/777-200ERSF)? Planes like the 777-200F, A330-200F do not have plugged windows which contradicts your last statement.

I see the edits, but this answer is still not right. AFAIK, the plane cited was built new as a cargo plane, as the same class 777-200F. It is not a P2F conversion. Further, this answer doesn't address the exit doors. Doors are removed and reskinned in some situations (A321P2F).

If you zoom in on the pic of the one in the OP you can make out the window frames in spots. The Expediter was not built as a purpose built freighter with its own purpose built windowless fuselage. That's why the exit doors are still there.  Because so are the window openings.

Adapting an airframe for a new mission requires a series of cost-benefit decisions. Removing the exits from the fuselage would require a complete set of structural testing to gain certification, which is a lot of time and money for little benefit when you can just paint the window. Plus, if you design out the exits you can't reconfigure the airplane back to passenger use.
The usual solution is to put blank plates in the place of the windows and emergency exits, which is the case here.

Wouldn't you also need alternative tooling, manufacture of different components and new production processes?

This variant already has the cabin windows designed out, though - so why not the overwing exits as well?

They aren't designed out, the windows are still there, the seams are hard to see.

@DaveGremlin It's not that bad with metal fuselages, because it was one piece to begin with: they skip the step of cutting the windows out. The story may be different with carbon fiber.

You'd think that removing the windows would strengthen the hull (since adding windows weakens it).

@RonJohn No, because the structure was reinforced back to the same strength. When removing the window, they also remove the window frame and doubler, which where a lot of the mass savings are. Second, it changes the stress distribution of the fuselage, which needs to be re-analyzed. As real example, Southwest Flight 2294 blew a hole due to cracking because Southwest didn't cut a hole in the fuselage for an antenna. This caused the panel to have increased stiffness, which led to stress concentration at an adjacent panel. Boeing knew about this but underestimated the cycles needed to crack.

@user71659 "which led to stress concentration at an adjacent panel." This reminds me of the deHaviland Comet accident.


text:
Why does spoiler extension cause straight-wing Learjets to pitch down, rather than up, and why did it take so long to discover this?
Straight-wing Learjets (the 23, 24, 25, 35, and 36), the first generation of the popular business-jet series, are (especially when not equipped with any of the many first- and third-party wing modifications developed for these aircraft) extremely unforgiving to fly, with a well-deserved reputation for killing pilots who, whether accidentally or deliberately, pushed their aircraft’s limits.
One of the factors contributing to this is their extreme susceptibility to mach tuck (a product of a wing design which proved inordinately prone to airflow separation with the slightest provocation, something also playing a part in the unusual ease with which a stock straight-wing Learjet can be inadvertently stalled), a problem aggravated by one of the steps originally called for when recovering from an accidental overspeed or overmach.1
Namely, the extension of the aircraft’s spoilers.
This would, intuitively, seem to be a valid technique for recovering from a high-speed dive, for three reasons:

The first, and most obvious, is that they greatly increase the drag generated by the aircraft, tending to slow it down and aid the pilots in regaining control.
On the pitch side of things, the spoilers - and the drag they generate when extended - are on top of the wings; as such, extending the spoilers should produce a torque on the wing (and, through it, the rest of the aircraft) tending to pitch the aircraft up.
Also, as an aircraft’s spoilers are mounted well back from the wing’s leading edge, extending them dumps the lift from the rear portion of the wing, but not the front portion; this moves the aircraft’s center of lift forwards, creating an additional pitch-up moment.

Intuitively, it seems like this effect should be especially strong for a straight-winged aircraft, like a first-generation Learjet.  As an aircraft’s spoiler panels are generally concentrated in the inboard portion of the wing (so as not to cause roll-control-impairing flow separation over the ailerons), an aircraft with swept wings could, conceivably, have its outer wings far enough behind its inner wings to move the overall center of lift behind the center of the area of spoiler-dumped lift (thereby generating a pitch-down moment upon spoiler extension); a straight-winged aircraft would be immune to this particular problem.

Both of the pitch-up tendencies thereby generated should also help to slow the aircraft even further.

Indeed, for most aircraft, extending the spoilers in flight does indeed cause the aircraft to pitch up and slow;2 this is not, however, the case for straight-wing Learjets, which, instead, pitch strongly down - and speed up even further - upon spoiler extension.
To quote the NTSB (the emphasis, however, is my own):

Although several revisions to the [Learjet 24] AFM were issued on and following October 1, 1980, none of the revisions were found attached to the copy of the AFM or in and around the wreckage.  The following revision was approved on October 1, 1980.

These speeds shall not be deliberately exceeded in any flight condition except where higher speed is specifically authorized for flight tests of pilot training or in approved emergency procedures.
WARNING: Do not extend the spoilers, or operate with spoilers deployed, at speeds above VMO/MMO [sic] due to the significant nose down pitching moment associated with spoiler deployment.
RECOVERY FROM OVERSPEED
If VMO or MMO is inadvertently exceeded:
WARNING: Do not extend the spoilers, or operate with the spoilers deployed, at speeds above VMO/MMO [sic] due to the significant nose down pitching moment associated with spoiler deployment.

Thrust Levers - IDLE.
Level wings if required.
Rotate nose-up not to exceed 1.5 g’s.  [sic] [Pages 12-13 of the paper report; pages 15-16 of its PDF.  Here, the NTSB is quoting Gates Learjet's 1 October 1980 revision to the Learjet 24’s Airplane Flight Manual (AFM).]

[...]  The following extracts[,] regarding specific problem areas discussed in the [FAA’s] interim SCR report, were made available to the Safety Board [by the FAA] on May 8, 1981:

[...]
1) High Speed Characteristics
[...]
c. Extension of the spoilers at high speed causes a large nose down pitching moment.  For the Lear 35 D/F models, stick force required to hold airspeed with spoiler extension at VMO varies from 46 lbs. at aft c.g. to 84 lbs. at forward c.g.[.]  [Page 15 (18).  Here, the NTSB is quoting the FAA's 1980-81 special certification review (SCR) of the Learjet 24 and later.3]

If a pitch upset occurs near MMO, the airplane can accelerate rapidly into a region where the flying qualities are unacceptable.  Consider, for example, any type of nose down pitch axis malfunction (such as trim runaway, pusher hardover, autopilot hardover, etc.).  In this case, if the pilot restrains the control column, the pull force can go as high as 50-60 lbs. (80 lbs. for pusher malfunction.)[.]  Because of pilot reaction time (3 seconds according to 8110.10), [...] the speed will have increased beyond the limit Mach number.  If the pilot follows the AFM procedure for overspeed and deploys the spoilers (which is instinctive), the required pull force will increase an additional 50-80 lbs.  Also, because of the pitch instability due to Mach tuck, the pull force will continue to increase as speed increases.  Adding the maneuvering stick force required to pull 1.5 g, the total pilot force required for recovery can be as high as 150-200 lbs.[.]
The stick puller was installed to prevent Mach overspeed, but[,] in the event of a nose down pitch axis malfunction, and/or deployment of the spoilers, its 18 lb. pull becomes insignificant.
[...]
If, after the pilot notices the overspeed, he deploys the spoilers, or if aileron “snatch” rolls the airplane to an excessive bank angle, it may become impossible to recover.  [Pages 16-17 (19-20).]
[...]  If the flightcrew had deployed the spoilers at this point without instantly reducing thrust, the control column pull forces would have increased and the speed instability and roll control could have progressed to the point where it would have become impossible to recover the aircraft. [Page 22 (25).]
11. The flightcrew probably deployed the spoilers at some point beyond airspeed limits in an attempt to regain control of the aircraft; this probably imposed excessive control wheel forces and prevented recovery of the aircraft. [Page 26 (29).]
[...]  It was also noted that, “...extension of the spoilers is not a viable procedure to prevent acceleration in a nosedown trim runaway condition.  Extension of the spoilers at Vmo with full nosedown trim required an elevator force estimated at 120 to 140 pounds to maintain level flight.  At 250 knots, the elevator force was measured at 98 pounds with full nosedown trim and spoilers extended.”[.]
The investigation of these accidents prompted research related to the following key areas:
[...]
(2) Use of spoilers in a high speed recovery; [Page 43 (45).  In the first paragraph, the NTSB is quoting the NTSB's 1979 study of Learjet performance characteristics.  This last extract is from an appendix discussing the susceptibility of straight-wing Learjets to loss of control at high altitudes and/or airspeeds.]

Also, recall the date of the revision to the Learjet 24’s AFM which changed the overspeed-recovery procedure from “extend the spoilers” to “wait, no, no, don’t extend the spoilers”4: 1 October 1980.
The Learjet 23 was certificated, and entered service, in 1964; the Learjet 24 in 1966; the Learjet 25 in 1967; and the Learjet 35 and 36 in 1974.  Indicating that the spoiler-induced pitch-down moment of straight-wing Learjets was neither discovered during initial flight testing, nor in many years (nearly a decade and a half for the Learjet 23) of service, only being brought to light by special flight tests in May 1979 resulting from the NTSB’s investigation of an October 1978 crash of a Learjet 25.
Why do straight-wing Learjets pitch down rather than up when their spoilers are extended, and why was this not discovered during initial flight testing, or for many years thereafter?

1: Another aggravating factor was the susceptibility of early Learjets to autopilot malfunctions which could cause large, uncommanded pitch control inputs.  Yet another aggravating factor was the fact that the Learjet 24 and 25 were originally certificated with an excessively high service ceiling (51 kft), an altitude at which both aircraft were far into their coffin corner, leaving very little margin of safety between the aircraft’s stall speed and its maximum safe mach number (this one was permanently corrected by a 1981 airworthiness directive that limited the Learjet 24 and 25 to a 45-kft maximum altitude, although they remained unforgiving even outside the coffin corner).
2: Assuming, of course, that the aircraft has sufficient airspeed and angle-of-attack reserve to do this without stalling.
3: The Learjet 23 was not included in the review, as the focus of the SCR was the Learjets certificated under 14 CFR 25, which the Learjet 23 predates; however, the conclusions reached by (and the airworthiness directives issued as a result of) the SCR are also applicable to the Learjet 23, which is extremely similar to the Learjet 24 and 25.
4: I might be paraphrasing a bit here.

It's not straight wing--the leading edge is swept.

"So long to find it" us primarily opinion based, and the question would be better without it.

You get an automatic +1 for actually researching your question. Thank you

You know it’s @Sean, when you see the question is long and well researched than the answer.

To think that spoilers generate pitch up moment because it sticks up is an over (and incorrect) simplification. The torque generated by the drag is also minimally contributory to the overall pitching moment. Rather, let me break it down into the following factors, then we can go back to why the Lear 25 may experience pitch down when its spoilers are deployed.
1. Pressure distribution due to spoiler on 2D section
Spoiler attached to the upper surface of an airfoil will cause the flow to separate, thereby resulting in the loss of lift and in the increase of drag. The effect of the spoiler, however, are not local; it changes the pressure distribution of both the upper and lower surface. Take a look at a typical pressure distribution with spoiler (Ref. ESDU Item 90030):

As you can see, on the upper surface, the effect is a net down load ahead of the spoiler (located at roughly 50% chord) and a suction plateau behind it. In this particular example, it would create a net nose down moment about the quarter chord. On the lower surface as a whole, there is an increased down load, resulting in a net nose up moment about the quarter chord. Depending on geometry of the airfoil and the chord-wise location of the spoiler, which change the relative strengths of the moments, you can get a net nose-up or nose-down moment.
The effect of chord-wise location is explored in this ARC report using an RAE100 symmetric airfoil. I've summarized the pitching moment result about the quarter chord below. As the spoiler moves aft (xs/c), there is an increasing nose-up pitching moment.

2. Wing sweep and spanwise location of spoiler
The wing of an aircraft flying through transonic speed is generally swept. For most transport category aircraft, the ground spoilers are located inboard while the flight spoilers are located mid-span. This is illustrated using a Gulfstream II shown below:

It's pretty intuitive to understand that the more outboard the lift loss, the more nose up pitch the aircraft experiences due to the sweep back at, say, 25% MAC. This is indeed the case from sources such as the NASA Technical Paper 1419. In it, you can see the pitch up increasing progressively as more outboard spoilers are deflected.
A note-worthy source is the NTSB accident report on the Gulfstream II of 1975, which I quote (boldened texts are from me):

Aerodynamic pitching moments caused by spoiler deployment were relatively small throughout the Mach number range to 0.80. The maximum operating speed for the airplane is 0.72 Mach. Deployment of the flight spoilers resulted in a small noseup pitching moment. Deployment of the ground spoilers resulted in a small nosedown pitching moment. The net effect of deploying both ground and flight spoilers reduced the incremental pitching effect to approximately zero or very slightly nosedown.

3. Downwash on the tail
When the wing loses lift, the downwash on the tail would be changed. An increasing downwash implies a nose-up moment from the tail; a decreasing downwash implies a nose-down moment from the tail.
Unfortunately, I have yet to find a non-proprietary literature source that documents the change in downwash from spoiler deployment. My intuition is that, due to the decrease in lift, we would expect to see a reduction in downwash.
4. Conclusion
Now let's take a look at Learjet 25/35 (3-view of Learjet 35 below):

The jet is gently swept about the quarter chord. It has only one pair of spoilers located inboard. Depending on the relative contributions of the above factors, it is not difficult to see why the model may experience pitch-down with its spoilers deflected.